In recent years, rewritable optical discs and write-once optical discs having large capacities such as BD-REs (Blu-ray Disc Rewritable) and BD-Rs (Blu-ray Disc Recordable) have been widespread. With BDs, a defect management system is employed also for BD-Rs, which are write-once optical discs, and the data recording reliability is ensured by replacing defect blocks with spare areas provided along the inner periphery and the outer periphery. Moreover, upon receipt of a data recording request to an already recorded area, the area is replaced with an unrecorded portion of a user data area, realizing logical overwrite (or pseudo overwrite).
A logical structure of a double-layer BD-R is shown in FIG. 13 (see Non-Patent Document No. 1). In a BD-R, user data areas for recording user data, spare areas for replacing defect blocks of user data areas, and a DMA (Disc Management Area) and a TDMA (Temporary Disc Management Area) for recording disc management information are allocated. Note that a TDMA is referred to also as a temporary management information area.
Disc management information is recorded in a TDMA until the disc is finalized, and is recorded in a DMA when the disc is finalized.
As shown in FIG. 14, in a TDMA, a plurality of TDMSs (Temporary Disc Management Structure) are recorded one at a time (see Patent Document No. 1). Where the recording mode of the disc is the sequential recording mode, a TDMS includes a TDFL (Temporary Defect List), an SRRI (Sequential Recording Range Information), and a TDDS (Temporary Disc Definition Structure). TDFL is used mainly as a defect list for managing replacement areas for defect areas on the disc. SRRI mainly includes management information on a recording area called SRR (Sequential Recording Range). TDDS includes definition structure information of the disc such as the arrangement information of TDFL and SRRI and the capacity of the spare area. Note that TDMS is referred to also as temporary management information, and TDFL is referred to also as a (temporary) defect list.
The operation of logical overwrite will be described using FIG. 15. When overwriting data A′ in block P when there is data A recorded in block P, data A′ is recorded in block Q at the beginning of the unrecorded area, and a TDMS is additionally recorded in the TDMA wherein the TDMS includes, as a TDFL, a defect list to which an entry is added indicating that block P has been replaced with block Q. Then, upon receipt of a reproduction request for block P, the control refers to the defect list to confirm that block P has been replaced with block Q, and accordingly reproduces block Q to obtain data A′. Thus, logical overwrite is realized through replacements using a defect list.
With such logical overwrite, when a file is overwritten, the contents thereof as of before the file is overwritten can no longer be obtained, which will now be described using FIG. 16. In FIG. 16, each FE (File Entry) is meta data including attributes of a file, the position at which the contents of the file are recorded, the size of the file, etc. Physically recorded contents are the contents actually recorded on the disc, and logically recorded contents are the contents that reflect the results of logical overwrite and that can be referred to from outside the information recording/reproduction device. Where File-A and File-B are recorded as shown in FIG. 16(a), when File-A is overwritten with File-A′ as shown in FIG. 16(b), the contents of File-A′ are recorded in an unrecorded area, after which FE of File-A is logically overwritten with FE of File-A′. As a result, as shown in FIG. 16(b), it is no longer possible to refer to FE of File-A from outside the information recording/reproduction device, whereby the position at which the contents of File-A are recorded and the size of File-A become unknown, and it is therefore no longer possible to obtain the contents of File-A.
In contrast, Patent Document No. 2 discloses a method for obtaining contents before an overwrite where a file has been overwritten. Patent Document No. 2 is directed to a configuration where a DDS (TDDS) includes a restoration DLT (TDFL) address, wherein the past state is restored by bringing it back to the previous DLT (TDFL) based on the restoration DLT (TDFL) address.